Art of protectively treating metals



Patented July 15, 1930 UNITED STATES PATENT OFFICE ARTHUR AREN'T, OF DESMOINES, IOWA, ASSIGNOR TO ARTHUR AREN'T LABORATORIES, INC., OF DESMOINES, IOWA, A CORPORATION OF IOWA ART OF PROTECTIVELY TREATING METALSNo Drawing. Application filed December This invention relates to art ofprotectively treating metals; and in particular it relates to a processof providing metal or metallized surfaces with a thin coating of a metalresistantto corrosion, wherein the protective metal is employed in asubstantially non-aqueous solution, such solution being applied in anysuitable manner to the metallic surface to be treated, whereupon theprotective metal is deposited in the form of a protective coating orskin. The invention also comprises novel compositions of matter usefulin employing and carrying. out the process, and also vnovel productsresulting from the process.

For the protection of structures and articles made of iron or steel, forexample, against corrosion due to atmospheric and other influences,numerous methods of treatment have been proposed heretofore in the artand some of these have gone into practical use with some degree ofsuccess. In particular, it has been proposed to provide the surface tobe protected with a metal or alloy coating or skin which is either moreresistant to corrosion than the underlying metal or is preferentiallyattacked by the corroding agencies involved. Thus, galvanizing,sherardizing, and tinning are methods widely used for this purpose. Insome special arts, as in the manufacture of gun barrels for example,protective coatings of other metals, including antimony, have beenemployed. The covering of iron and steel surfaces with a coating of leadhas also been practiced to some extent. I

The foregoing prior methods of protecting metal surfaces all involvespecial methods of treatment which are more or less diflicult andcomplicated. Usually it is essential to carry out the treatingprocesswith the aid of heat at relatively high temperatures, while in someinstances electroplating from aqueous baths of special composition undercarefully regulated conditions has been resorted to.

The present "applicant has discovered that by proceeding in accordancewith the principles of the invention hereinafter to be more fullyexplained, excellent protection of corrodihle metallic surfaces may beattained'in a relatively simple manner and in many-cases at lower costthan has vbeen possible hereto 8,1925. Serial No. 74,184.

fore, a superior degree of protection being afforded and certainadditional advantages being realized.

In general, the process of the present invention comprises subjectingthe surface of metal to be protected to the action of a non-aqueoussolution of a compound of another metal which is more resistant tocorrosion than the first mentioned metal in such manner that such moreresistant metal is deposited from its solution upon the first metal.Usually the protective metal used is ele'ctronegative with respect tothe metal upon which it is to be deposited. More specifically, the novelprocess comprises subjecting iron or steel surfaces to the action atordinary temperatures of a solution of a non-ferrous metal compound,especially a heat stable salt of an antimony group metal such asantimony it- 'self, in a non-aqueous solvent, which is fluid atatmospheric pressure and temperature and which is capable of dissolvingthe metal compound in suflicient quantity and also capable of releasingthe protective metal Without the aid of an electric current, when thesolution is brought into contact with the metal surface to be protected,in such manner that an adequate film or like coating of the non-ferrousmetal is formed on the iron or steel. The iron or steel may have beenpreviously provided with a coating of another metal more electropositivethan said non-ferrous metal, as by galvanizing, sherardizing, or othermetallizing process; in which case the protective coating of the presentnovel process may be superposed upon such previously applied metalcoating.

.Without intending thereby to limit the scope of the invention,reference will be made hereinafter more particularly to the employmentof antimony compounds in accordance with the principles of theinvention, it being understood that this is merely for the purposes ofexplaining and illustrating the underlying principles here involved.With this same purpose in view, certain specific nonaqueous liquidsolvents will be mentioned hereinafter, but it is to be understood thatthese are merely typical of non-aqueous sol- 10a vents that may beemployed in practicing the invention.

In a specific example embodying the rinciples of the invention, it willbe-assume that sheet iron is to be treated in accordance with theprocess of the invention. The term iron is used in the presentspecification and claims to include not only i'ron strictly speaking butalso steel in its various forms. It has been found that the inventioncan be practiced to greatest advantage if the sheet iron has alreadyreceived a coating of a metal, such as ZlIlC, that 1s moreelectro'positive than-iron.

Therefore, if the iron has not already re-,

ceived such a coating, this may advantageously be applied by a suitablegalvanizing or sherardizing treatment which, considered alone, forms no.part of the present invention and requires no specific description here,

suitable methods of galvanizing and sherardizing being well known in theart. Assuming that in this instance the sheet iron has been galvanized,the next step is to apply to it a solution of antimony trichlorid in alight mineral oil distillate, such as kerosene, the solution mostdesirably containing about three quartcrsof a pound of pure anhydrousantimony trichlorid crystals per gallon of ordinary commercial keroseneof good grade, or about a 10 per cent antimony trichlorid solution inkerosene. This is approximately a saturated solution of antimonytrichlorid in kerosene and it is characterized by a bluish pink orpurplish color. The content of combined antimony is around 5 per cent.The particular manner of applying this solution to the galvanized ironis not material, generally speaking. The solution may be brushed orsprayed on the galvanized iron, for example; or the galvanized iron maybe dipped into the treating solutidn. Good results can also be obtainedby bringing vapors of the solution into contact with the surface to betreated, the antimony salt being carried by the vapors in sutlicientquantity to produce the desired plating effect. Where this method isused, vaporization of the solution may be hastened by application ofmoderate heating.

Whatever method of application is employed, it is unnecessary to applyheat to the metal surface being treated in order to bring about thereaction by which the desired deposit of antimony is obtained on thegalvanized iron surface. This reaction takes place very rapidly atordinary room temperature merely upon contacting the solution with saidsurface. Progress of the reaction is indicated by a distinct darkeningof the galvanized iron surface which ecomes almost black after contactwith the solution for a short time, that is for a few seconds orminutes. In practice it is suflicient simply to dip the galvanized ironinto the treating solution and withdraw it therefrom immediately orafter a few moments, after which the treated 1 tion.

Where desired, the deposit may be produced by electroplating methods asdistinguished from thesimple dipping operation above described.

The dark colored protective metal coating obtained in the manner aboveset forth is tenaciously adherent .and extremely uniform in character,completely covering the original metal surface in a continuous film ofgreat uniformity and protective power. It adds greatly to the life ofthe metal sheet, being much more inert and resistant to corrosiveinfluences than either the zinc of the galvanizing coat or theunderlying iron. This makes it possible to employ the treated sheetmetal in many situations where it is exposed to corrosive liquids orgases that would rapidly destroy galvanized iron not treated inaccordance with the present process; For example, the protected metalresulting from the new rocess can be exposed for long periods 0 time tosea air, or even to sea Water or other salt brines without substantialdeterioration, as contrasted with the very rapid referring hereintotheprotective metal coating obtained by the process of the invention,"it isto be understood that this language is used in a broad sense to includealso an alloy of the protective metal with the underlying metal base ifin fact this is actually formed to a greater or less extent.

It has also been found that providing galvanized iron with an antimonyfilm coating in the manner above described not only greatly increasesthe resistance of the galvanized iron to corrosion, but it also has theeffect of enabling paint to'adhere directly to the surface thereof,whereasheretofore it has been necessary, in applying paint to galvanizediron and steel, to apply first a coat of sizing in order to render thepaint coating properly adherent with the permanency demanded by suchconditions as those to which metal signboards and the like are exposedin use. Thus, the invention is applicable with great advantage to thetreatment of previously manu- -factured galvanized sheet iron in theconstruction of sign-boards and the like, the present novel. treatmentof the sheet metal for this purpose being simply substituted for theusual sizing operation with the two-fold effect not only of ensuringpermanent adherence of the subsequently applied paint coat but also ofgreatly prolonging the life of the sign-board.

The treatment of galvanized sheet iron for sign-boards by the process ofthe invention is of course merely typicalof many uses to which theinvention may be put. Thus, other manufactured articles and materialscommonly made of galvanized iron or steel, such, for example, as gutterpipes and spouting, wire fencing,- barbed wire, and iron and steel wiregenerally, can be madevery resistant to rust and other forms ofcorrosion to which they are commonly subject by the simple and rapidtreatment above described whereby they are provided with a protectiveantimony coating. The comparative rapidity with which these variousmanufactured articles of ordinary galvanized iron often corrode andotherwise deteriorate in use, especially where exposed to weather in aircontaminated with industrial gases, for example, is well known. Theprotective film of antimony superposed on the zinc gives a compositeprotective coating which is resistant to such destructive agencies andgives the protected metal a much longer life than ordinary galvanizedmetal.

In the foregoing specific example, reference has been made to the use ofpure anhydrous antimony trichlorid crystals because .this form ofantimony trichlorid is for various reasons the most desirable to employ.So-called butter of antimony, or-other commercial form of antimonouschlorid that is sufiiciently low in moisture content to-enable it todissolve sufficiently in the non-aqueous solvent employed may be used,but generally speaking they are less desirable than the pure anhydrouscrystals because of the greater likelihood that free hydrochloric acidwill be present in the treating operation. The fact that the solution issubstantially without content of. free hydrochloric or other acidcorrosive to the surface to be protected is an im-' portant andadvantageous characteristic of non-aqueous solutions of the type mostdesirable for use in practicing the present invention.

Neither is it to be inferred that the invention is confined to theemployment of antimony trichlorid or other antimony compound. Whileantimony trichlorid oifers special advantages and is preferred,compounds of other metals soluble in non-aqueous solvents may beemployed and analogous efi'eets obtained. Thus, resinates or oleates ofother relatively corrosion-resistant metals such as copper and lead, forexample, are soluble in-various non-aqueous solvents such as hydrocarbonoils, for instance, and can be similarly used.

The employment of a light hydrocarbon solvent such as kerosene is to beparticularly recommended, but this specific type of nonaqueous solventis not essential in the broad er aspects of the invention. Thus,assuming the use of antimony trichlorid, solutions thereof in benzol,acetone, amyl acetate, or ethyl acetate, or in mixtures of such of theseas are miscible, have been found to function in a manner similar to thekerosene solution hereinabove described. Benzol is especially suitableas it will take up as much as two and one-half pounds of anhydrousantimony trichlorid per gallon. This strong solution may be diluted, asis frequently desirable, with more benzol or with kerosene.

Instead of applying the treatingsolution to a metal body that hasalready been provided with a protective coating, as by galvanizing, itis feasible and in many cases desirable to apply it directly to theunprotected metal. Thus, ordinary iron or steel sheets, wire, bars, andother articles, may be provided with a resistant protective coating ofantimony by direct application of non-aqueous solutions thereof. Theaction at ordinary room temperature isusually somewhat slower, however,than where the iron has been first galvanized.

Not only does the use of a non-aqueous solvent permit more readydeposition of the protective metal from solution, but furthermore itmakes possible the employment of salts, such as antimony trichlorid,that are insoluble in water except with the aid ofv strong acids,alkalis or other special assisting agent. The term non-aqueous is not tobe construed too narrowly, the presence of such slight amount ofmoisture in the solution being permissible as will not causebydrolyzation and resultant deposition of basic compounds therefrom.

What I claim is: v

1. The process of protecting metal surfaces against corrosion whichcomprises depositing antimony on such surface by contacting therewith asolution of antimony trichlorid in a hydrocarbon solvent thereof.

2. The process of protecting metal surfaces against corrosion whichcomprisesdepositing antimony on such surface by'contacting therewith asolution of antimony trichlorid in kerosene.

3. The process of protecting galvanized iron from corrosion whichcomprises applyrosion metal surfaces electropositive to antisolution ofan antimony tially non-aqueous liquid solvent which is .mainlyhydrocarbon in character until said mony group metals which comprisesproviding such a surface with an adherent protective coating containinga metal of the antimony groupby contacting with said surface a' solutionof an antimony group metal salt in a substantially non-aqueous liquidsolvent thereof until said coating is formed,

acid content corrosive to said surface.

8. The process of protecting against corrosion metal surfaceselectropositive to antimony which comprises providing such a surfacewith an adherent protective coating containing antimony by contactingwith said surface a solution of, an antimony salt in a substantiallynon-aqueous liquld solvent thereof until said coating is formed, saidsolution being substantially without free acid content corrosive to saidsurface.

9. The process defined in claim 8, further characterized by the factthat said solution contains at least about 5 per cent of combinedantimony.

, 10. The process of protecting zinc-covered metallic surfaces againstcorrosion which comprises contacting such a surface with a salt in asubstansurface is provided with an adherent protective coatingcontaining antimony, said signature.

- ARTHUR ARENT.

5 said solution being substantially without free 1 solution beingsubstantially without free acid I content corrosive to said surface.

11. Theprocess defined in claim 10, further characterized by the factthat the solution employed contains at least about 10 per cent ofantimony trichloride.

12. The process of protecting against corrosion metal surfaceselectropositive to antimony which comprises a p surface a solutionprepare by dissolving anhydrous antimony trichloride crystals in anon-aqueous solvent,-said solution being substantially without free acidcontent corrosive to said surface.

13. The process defined in claim 6, further characterized by the factthat the solvent employed comprises benzol.

ying to such a

